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Background: Cowpea [Vigna unguiculata (L) Walp.] is one of the Paraguayan rural families' main crops, serving as an essential protein and carbohydrate source. Cowpea aphid borne mosaic virus (CABMV) and cowpea severe mosaic virus (CPSMV) were identified infecting cowpea plants. Disease control caused by both viruses is difficult because there is no information about local cowpea resistant cultivars and vector control is not practical. Methods: In the present work, sixteen cowpea genotypes/cultivars were mechanically inoculated with local isolates of CABMV and CPSMV to identify resistant genotypes/cultivars that can be used in breeding programs. Virus infections were determined by symptoms expression and confirmed by PTA-ELISA. Result: Genotypes Arroz rojo (V. angularis), TVu 379, TVu 382, TE94-256-2E and TE97-309G-9 were resistant to CABMV. Genotypes Arroz rojo (V. angularis), CNCX-698-128F, TVu 379, TVu 382, TVu-3961, TE97-309G-9 and TE97-309G-3 were resistant to CPSMV. Overall, this study showed that local cowpea cultivars do not offer any resistance to virus infection and the need for resistant germplasms for cowpea breeding programs in the country. [ABSTRACT FROM AUTHOR]

Papaya sticky disease is caused by the association of a fusagra-like and an umbra-like virus, named papaya meleira virus (PMeV) and papaya meleira virus 2 (PMeV2), respectively. Both viral genomes are encapsidated in particles formed by the PMeV ORF1 product, which has the potential to encode a protein with 1563 amino acids (aa). However, the structural components of the viral capsid are unknown. To characterize the structural proteins of PMeV and PMeV2, virions were purified from Carica papaya latex. SDS-PAGE analysis of purified virus revealed two major proteins of ~40 kDa and ~55 kDa. Amino-terminal sequencing of the ~55 kDa protein and LC-MS/MS of purified virions indicated that this protein starts at aa 263 of the deduced ORF1 product as a result of either degradation or proteolytic processing. A yeast two-hybrid assay was used to identify Arabidopsis proteins interacting with two PMeV ORF1 product fragments (aa 321–670 and 961–1200). The 50S ribosomal protein L17 (AtRPL17) was identified as potentially associated with modulated translation-related proteins. In plant cells, AtRPL17 co-localized and interacted with the PMeV ORF1 fragments. These findings support the hypothesis that the interaction between PMeV/PMeV2 structural proteins and RPL17 is important for virus–host interactions. [ABSTRACT FROM AUTHOR]

Viruses were discovered as agents of disease in the late 19th century, but it was not until the 1930s that the nature of these agents was elucidated. Nevertheless, as soon as viral diseases started to be recognized and cataloged, there were attempts to classify and name viruses. Although these early attempts failed to be adopted by the nascent virology community, they are evidence of the human compulsion to try to organize the natural world into well-defined categories. Different classification schemes were proposed during the 20th century, but again none were widely embraced by virologists. In 1966, with the creation of the International Committee on Nomenclature of Viruses (eventually renamed as the International Committee on Taxonomy of Viruses), a more organized effort led to an official taxonomy in which viruses were classified into families and genera. At present, a much better understanding of the evolutionary relationships among viruses has led to the establishment of a 15-rank taxonomy based primarily on these evolutionary relationships. This review of virus taxonomy will be centered on the tobacco mosaic virus (TMV), the agent of the disease studied by Dmitry Ivanovsky and the first virus to be recognized as such, which was often historically at the center of major advancements in virology during the 20th century. [ABSTRACT FROM AUTHOR]

An increasing number of plant species have been recognized or considered likely reservoirs of viruses transmitted by Brevipalpus mites. A tiny fraction of these viruses, primarily those causing severe economic burden to prominent crops, have been fully characterized. In this study, based on high-throughput sequencing, transmission electron microscopy analyses of virions in plant-infected tissues, viral transmission experiments, and the morphoanatomical identification of the involved Brevipalpus mites, we describe molecular and biological features of viruses representing three new tentative species of the family Kitaviridae. The genomes of Solanum violifolium ringspot virus (SvRSV, previously partially characterized), Ligustrum chlorotic spot virus (LigCSV), and Ligustrum leprosis virus (LigLV) have five open reading frames (ORFs) > 500 nts, two distributed in RNA1 and three in RNA2. RNA1 of these three viruses display the same genomic organization found in RNA1 of typical cileviruses, while their RNA2 are shorter, possessing only orthologs of genes p61 , p32 , and p24. LigCSV and LigLV are more closely related to each other than to SvRSV, but the identities between their genomic RNAs were lower than 70%. In gene-by-gene comparisons, ORFs from LigCSV and LigLV had the highest sequence identity values (nt sequences: 70–76% and deduced amino acid sequences: 74–83%). The next higher identity values were with ORFs from typical cileviruses, with values below 66%. Virions of LigLV (≈ 40 nm × 55 nm) and LigCSV (≈ 54 nm × 66 nm) appear almost spherical, contrasting with the bacilliform shape of SvRSV virions (≈ 47 nm × 101 nm). Mites collected from the virus-infected plants were identified as Brevipalpus papayensis, B. tucuman , and B. obovatus. Viruliferous B. papayensis mites successfully transmitted LigCSV to Arabidopsis thaliana. SvRSV, LigCSV, and LigLV seem to represent novel sub-lineages of kitaviruses that descent on parallel evolutionary branches from a common ancestor shared with the tentative cile-like virus hibiscus yellow blotch virus and typical cileviruses. Biological and molecular data, notably, the phylogenetic reconstruction based on the RdRp proteins in which strong support for monophyly of the family Kitaviridae is observed, mark an advance in the understanding of kitavirids. [ABSTRACT FROM AUTHOR]

Carlaviruses are plant‐infecting viruses with flexuous filamentous particles of approximately 650 nm in length and a positive single‐stranded hexacistronic RNA molecule as the genome. In this study, we analysed 14 samples of brassicas plants, reportedly affected by carlaviruses, that were collected in distant and edaphoclimatic distinct regions in Brazil. The genomes of four viral isolates detected in leaf kale (Brassica oleracea var. acephala) plants displayed the typical genomic organization of carlaviruses, subdivided into two contrasting identity profiles. Isolates T25, T107, and T110 showed a higher sequence identity among them (c.93%) than with T90 (c.67%), which had the highest nucleotide sequence identity (85.2%) with the only documented genomic fragment, approximately 1 kb of the RNA 3′‐end, of cole latent virus (CoLV). Identity values among the other three isolates and CoLV were consistently lower than 78.6%. Nucleotide and amino acid sequence identity values of the replicase cistron of the isolates T25 and T90 are below the threshold for species demarcation in the genus Carlavirus. Upon mechanical transmission, these two isolates induced different symptoms in brassicas and solanaceous plants. Overall, data indicated that these viruses belong to two related but distinct species of carlaviruses. While T90 was recognized as an isolate of CoLV, the remaining isolates were considered members of a new tentative carlavirus named Cole mild mosaic virus (CoMMV). Current work provides convincing support for the taxonomic status of the species Cole latent virus, enlarges the known diversity of carlaviruses, and makes available new molecular tools to improve surveys of brassica‐infecting viruses. [ABSTRACT FROM AUTHOR]

The flat mite genus Raoiella Hirst (Tenuipalpidae) has attracted considerable research interest due to the rapid spread of Raoiella indica Hirst which feeds most commonly on species of palms (Arecaceae). Raoiella are frequently observed with their stylets inserted into the leaf stomatal openings, suggesting they feed on this site. Herein, we use transmission electron microscopy (TEM), scanning electron microscopy (SEM), low temperature scanning electron microscopy (LTSEM) and light microscopy (LM) to describe the mouthpart organization and the feeding behavior found in R. indica and R. bauchani Beard & Ochoa. The feeding mechanism is also discussed based on their distinctive morphological aspects. The structure of the gnathosoma of Raoiella generally agrees with the organization previously observed in Brevipalpus and Cenopalpus. As in other tetranychoid mites, there is no anatomical connection between the inter-stylet tube and the food channel, corroborating the theory that the stylets are used to pierce plant tissue (and assumedly inject saliva) but play no role in sucking up fluid from damaged host cells. As in Brevipalpus, the adoral setae are mechanoreceptors that may help guide the mite to the site for feeding. The ultrastructure of supracoxal setae e remains enigmatic. We also present observations of possible epidermal feeding on Phoenix roebelenii O'Brien (Arecaceae) for R. indica. Raoiella indica were shown to penetrate both the guard cells of the stomata and the epidermis of P. roebelenii, suggesting that feeding via the epidermis could be possible on this host plant. [ABSTRACT FROM AUTHOR]

Pepper yellow mosaic virus on Petunia hybrida, bean yellow mosaic virus on Viola odorata and Narcissus yellow stripe virus on Narcissus cyclamineus were identified in Brazil using RT-PCR. Serology, mechanical transmission, host range, and electron microscopy were used to study the viruses further. [ABSTRACT FROM AUTHOR]

Begomoviruses (family Geminiviridae) have a circular, ssDNA genome encapsidated in twinned icosahedral particles. Numerous begomoviruses infecting noncultivated malvaceous plants have been described, and evidence suggests that they may have given rise to some of the viruses currently found in crop plants. Here we describe an atypical begomovirus infecting ornamental Turk's hat plants (Malvaviscus arboreus, Malvaceae). Total DNA was extracted, and the viral genome was amplified by rolling‐circle amplification (RCA), cloned and sequenced. Sequence and phylogenetic analyses indicated that the virus corresponds to a new begomovirus phylogenetically related to other malvaceous‐infecting begomoviruses from Brazil, and for which the name malvaviscus yellow mosaic virus (MvYMV) is proposed. M. arboreus plants inoculated with MvYMV infectious clones showed bright yellow mosaic and the virus progeny was identical to the isolate inoculated, thus fulfilling Koch's postulates. Strikingly, MvYMV has a nanovirus/alphasatellite‐like nonanucleotide sequence (5′‐TAGTATTAC‐3′). Moreover, a short sequence located 5′ of the nonanucleotide potentially forms a minor hairpin structure embedded in the major hairpin. Intramolecular interactions involving the sequence of the atypical hairpin structure were predicted and functional analyses were conducted to assess its biological relevance, revealing that the MvYMV Rep protein recognises this unique replication origin but not the typical begomovirus origin. Thus, MvYMV is a begomovirus with an atypical origin of replication and naturally found in noncultivated malvaceous plants. [ABSTRACT FROM AUTHOR]

Abstract Background Citrus canker is a disease that has severe economic impact on the citrus industry worldwide. There are three types of canker, called A, B, and C. The three types have different phenotypes and affect different citrus species. The causative agent for type A is Xanthomonas citri subsp. citri, whose genome sequence was made available in 2002. Xanthomonas fuscans subsp. aurantifolii strain B causes canker B and Xanthomonas fuscans subsp. aurantifolii strain C causes canker C. Results We have sequenced the genomes of strains B and C to draft status. We have compared their genomic content to X. citri subsp. citri and to other Xanthomonas genomes, with special emphasis on type III secreted effector repertoires. In addition to pthA, already known to be present in all three citrus canker strains, two additional effector genes, xopE3 and xopAI, are also present in all three strains and are both located on the same putative genomic island. These two effector genes, along with one other effector-like gene in the same region, are thus good candidates for being pathogenicity factors on citrus. Numerous gene content differences also exist between the three cankers strains, which can be correlated with their different virulence and host range. Particular attention was placed on the analysis of genes involved in biofilm formation and quorum sensing, type IV secretion, flagellum synthesis and motility, lipopolysacharide synthesis, and on the gene xacPNP, which codes for a natriuretic protein. Conclusion We have uncovered numerous commonalities and differences in gene content between the genomes of the pathogenic agents causing citrus canker A, B, and C and other Xanthomonas genomes. Molecular genetics can now be employed to determine the role of these genes in plant-microbe interactions. The gained knowledge will be instrumental for improving citrus canker control.

Despite the importance of viral strains/variants as agents of emerging diseases, genetic and evolutionary processes affecting their ecology are not fully understood. To get insight into this topic, we assessed the population and spatial dynamic parameters of citrus leprosis virus C (CiLV-C, genus Cilevirus , family Kitaviridae). CiLV-C is the etiological agent of citrus leprosis disease, a non-systemic infection considered the main viral disorder affecting citrus orchards in Brazil. Overall, we obtained 18 complete or near-complete viral genomes, 123 complete nucleotide sequences of the open reading frame (ORF) encoding the putative coat protein, and 204 partial nucleotide sequences of the ORF encoding the movement protein, from 430 infected Citrus spp. samples collected between 1932 and 2020. A thorough examination of the collected dataset suggested that the CiLV-C population consists of the major lineages CRD and SJP, unevenly distributed, plus a third one called ASU identified in this work, which is represented by a single isolate found in an herbarium sample collected in Asuncion, Paraguay, in 1937. Viruses from the three lineages share about 85% nucleotide sequence identity and show signs of inter-clade recombination events. Members of the lineage CRD were identified both in commercial and non-commercial citrus orchards. However, those of the lineages SJP were exclusively detected in samples collected in the citrus belt of São Paulo and Minas Gerais, the leading Brazilian citrus production region, after 2015. The most recent common ancestor of viruses of the three lineages dates back to, at least, ∼1500 years ago. Since citrus plants were introduced in the Americas by the Portuguese around the 1520s, the Bayesian phylodynamic analysis suggested that the ancestors of the main CiLV-C lineages likely originated in contact with native vegetation of South America. The intensive expansion of CRD and SJP lineages in Brazil started probably linked to the beginning of the local citrus industry. The high prevalence of CiLV-C in the citrus belt of Brazil likely ensues from the intensive connectivity between orchards, which represents a potential risk toward pathogen saturation across the region. [ABSTRACT FROM AUTHOR]

Senna rizzinii is a flowering shrub found mainly in the northeast region of Brazil. Here, we report the coding-complete genome sequence, particle morphology, mode of transmission, and the indicator host responses of an isolate of the putative allexivirus cassia mild mosaic virus (CaMMV) found in S. rizzinii. The virus was transmitted mechanically to Chenopodium amaranticolor, C. quinoa, Gomphrena globosa, which showed local lesions, and S. rizzinii, and S. occidentalis, which were infected systemically. It was also efficiently transmitted to S. rizzinii by grafting. Seed transmission was not observed. The near-complete genome sequence of the virus is 7829 nucleotides in length, containing six open reading frames (ORF), like other allexiviruses. [ABSTRACT FROM AUTHOR]

A list of plant species, in alphabetical order by their scientific name, and the viruses found naturally infecting them in Brazilian territory, with some comments, was prepared. The production of such a list was based on a yearly catalog of publications on plant viruses collected by the author, from 1926 to 2018. Listed species of viruses were those recognized by the International Committee on Taxonomy of Viruses (ICTV), but also those characterized and still waiting official recognition, were included. Several cases of putative viral diseases were listed for historical reasons expecting to raise interest for their clarification. This list includes 345 plants species belonging to 74 families naturally infected by plant viruses in Brazil. Fabaceae and Asteraceae had most virusinfected species, respectively 49 and 36. Until 2018, a total of 213 plant virus and 6 viroid species belonging to 57 genera and 22 families and 6 orders, officially recognized by ICTV, were found naturally infecting these plants. Begomovirus and Potyvirus genera have most representatives, with 45 and 42 species, respectively. There are 59 characterized plant viruses, up to species level, described in Brazil waiting for the inclusion in the ICTV Master Species List. One hundred and thirteen viruses were identified up to genus level but still uncharacterized, while four putative isometric viruses and eleven presumptive viral diseases ("unidentified") are included in the list. A reverse catalog, listing viruses and the plant species in which they were found is also included. [ABSTRACT FROM AUTHOR]

Passion fruit green spot and passion fruit sudden death are two reportedly distinct viral diseases that recurrently affect passion fruit (Passiflora spp.) groves in Brazil. Here we used a systematic approach that interconnects symptoms, transmission electron microscopy, RT-PCR detection assays followed by Sanger sequencing, and high-throughput sequencing of the RNA of affected passion fruit plants to gain insights about these diseases. Our data confirmed not only the involvement of cileviruses in these two pathologies, as previously suggested, but also that these viruses belong to the same tentative species: passion fruit green spot virus (PfGSV). Results revealed that PfGSV has a positive-sense RNA genome split into two molecules of approximately 9 kb (RNA1) and 5 kb (RNA2), which share about 50–70% nucleotide sequence identity with other viruses in the genus Cilevirus. Genome sequences of five PfGSV isolates suggest that they have more conserved RNA1 (<5% of nucleotide sequence variability) compared to RNA2 (up to 7% of variability) molecules. The highest nucleotide sequence divergence among PfGSV isolates and other cileviruses is in the genomic segment covering from the 5′-end of the RNA2 until the 5′-end of the open reading frame (ORF) p61 , which includes the ORF p15 and the intergenic region. This genomic stretch also harbors a novel orphan ORF encoding a 13 kDa protein presenting a cysteine-rich domain. High variability of 5′-end of the RNA2 in cileviruses is discussed in an evolutionary context assuming that they share putative common ancestors with unclassified arthropod-infecting single-strand positive RNA viruses, including mosquito-specific viruses of the group Negevirus (clades Nelorpivirus and Sandwavirus), and other viruses in the family Kitaviridae. [ABSTRACT FROM AUTHOR]

Physalis peruviana is a perennial solanaceous plant that has recently been established as a commercial crop in Brazil. This work reports the near-complete genome sequence, particle morphology, and plant host responses to a putative new sobemovirus, named "physalis rugose mosaic virus". The virus, characterized by isometric particles of ca. 30 nm in diameter, causes foliar symptoms of mosaic, malformation and blistering, accompanied by stunting. The near-complete genome sequence comprises 4175 nucleotides and contains five open reading frames that are similar to those of other sobemoviruses. In addition to P. peruviana, the new virus systemically infected Capsicum annuum, Nicotiana tabacum and Solanum lycopersicum by mechanical inoculation. Thus, this virus may cause disease in these crops in the field. [ABSTRACT FROM AUTHOR]

Leprosis is a serious disease of citrus caused by Citrus leprosis virus C (CiLV-C, genus Cilevirus) whose transmission is mediated by false spider mites of the genus Brevipalpus. CiLV-C infection does not systemically spread in any of its known host plants, thus remaining restricted to local lesions around the feeding sites of viruliferous mites. To get insight into this unusual pathosystem, we evaluated the expression profiles of genes involved in defense mechanisms of Arabidopsis thaliana and Citrus sinensis upon infestation with non-viruliferous and viruliferous mites by using reverse-transcription qPCR. These results were analyzed together with the production of reactive oxygen species (ROS) and the appearance of dead cells as assessed by histochemical assays. After interaction with non-viruliferous mites, plants locally accumulated ROS and triggered the salicylic acid (SA) and jasmonate/ethylene (JA/ET) pathways. ERF branch of the JA/ET pathways was highly activated. In contrast, JA pathway genes were markedly suppressed upon the CiLV-C infection mediated by viruliferous mites. Viral infection also intensified the ROS burst and cell death, and enhanced the expression of genes involved in the RNA silencing mechanism and SA pathway. After 13 days of infestation of two sets of Arabidopsis plants with non-viruliferous and viruliferous mites, the number of mites in the CiLV-C infected Arabidopsis plants was significantly higher than in those infested with the non-viruliferous ones. Oviposition of the viruliferous mites occurred preferentially in the CiLV-C infected leaves. Based on these results, we postulated the first model of plant/Brevipalpus mite/cilevirus interaction in which cells surrounding the feeding sites of viruliferous mites typify the outcome of a hypersensitive-like response, whereas viral infection induces changes in the behavior of its vector. [ABSTRACT FROM AUTHOR]

Background: A betabaculovirus (DisaGV) was isolated from Diatraea saccharalis (Lepidoptera: Crambidae), one of the most important insect pests of the sugarcane and other monocot cultures in Brazil. Results: The complete genome sequence of DisaGV was determined using the 454-pyrosequencing method. The genome was 98,392 bp long, which makes it the smallest lepidopteran-infecting baculovirus sequenced to date. It had a G + C content of 29.7 % encoding 125 putative open reading frames (ORF). All the 37 baculovirus core genes and a set of 19 betabaculovirus-specific genes were found. A group of 13 putative genes was not found in any other baculovirus genome sequenced so far. A phylogenetic analysis indicated that DisaGV is a member of Betabaculovirus genus and that it is a sister group to a cluster formed by ChocGV, ErelGV, PiraGV isolates, ClanGV, CaLGV, CpGV, CrleGV, AdorGV, PhopGV and EpapGV. Surprisingly, we found in the DisaGV genome a G protein-coupled receptor related to lepidopteran and other insect virus genes and a gp64 homolog, which is likely a product of horizontal gene transfer from Group 1 alphabaculoviruses. Conclusion: DisaGV represents a distinct lineage of the genus Betabaculovirus. It is closely related to the CpGV-related group and presents the smallest genome in size so far. Remarkably, we found a homolog of gp64, which was reported solely in group 1 alphabaculovirus genomes so far. [ABSTRACT FROM AUTHOR]

First detection of papaya ringspot virus-type W and zucchini yellow mosaic virus infecting Cucurbita maxima in Paraguay. Keywords: Carica papaya; Papaya ringspot virus; Potyvirus EN Carica papaya Papaya ringspot virus Potyvirus 451 451 1 02/24/22 20220201 NES 220201 In several Paraguay regions, papaya trees ( I Carica papaya i ) occur naturally in particular gardens and public spaces. [Extracted from the article]

Background: Antigen B (AgB) is the major protein secreted by the Echinococcus granulosus metacestode and is involved in key host-parasite interactions during infection. The full comprehension of AgB functions depends on the elucidation of several structural aspects that remain unknown, such as its subunit composition and oligomeric states. Methodology/Principal Findings: The subunit composition of E. granulosus AgB oligomers from individual bovine and human cysts was assessed by mass spectrometry associated with electrophoretic analysis. AgB8/1, AgB8/2, AgB8/3 and AgB8/4 subunits were identified in all samples analyzed, and an AgB8/2 variant (AgB8/2v8) was found in one bovine sample. The exponentially modified protein abundance index (emPAI) was used to estimate the relative abundance of the AgB subunits, revealing that AgB8/1 subunit was relatively overrepresented in all samples. The abundance of AgB8/3 subunit varied between bovine and human cysts. The oligomeric states formed by E. granulosus AgB and recombinant subunits available, rAgB8/1, rAgB8/2 and rAgB8/3, were characterized by native PAGE, light scattering and microscopy. Recombinant subunits showed markedly distinct oligomerization behaviors, forming oligomers with a maximum size relation of rAgB8/3>rAgB8/2>rAgB8/1. Moreover, the oligomeric states formed by rAgB8/3 subunit were more similar to those observed for AgB purified from hydatid fluid. Pressure-induced dissociation experiments demonstrated that the molecular assemblies formed by the more aggregative subunits, rAgB8/2 and rAgB8/3, also display higher structural stability. Conclusions/Significance: For the first time, AgB subunit composition was analyzed in samples from single hydatid cysts, revealing qualitative and quantitative differences between samples. We showed that AgB oligomers are formed by different subunits, which have distinct abundances and oligomerization properties. Overall, our findings have significantly contributed to increase the current knowledge on AgB expression and structure, highlighting issues that may help to understand the parasite adaptive response during chronic infection. Author Summary: Antigen B (AgB) is the major secretory protein of the Echinococcus granulosus hydatid cyst, the causative agent of cystic hydatid disease. Structurally, AgB is a multisubunit protein formed by 8-kDa subunits, but it is not known which subunits are secreted by a single parasite (cyst) and how they interact in the formation of distinct AgB oligomeric states. Here, we investigated AgB subunit composition and oligomeric states in individual samples from bovine and human cysts. We identified AgB8/1, AgB8/2, AgB8/3 and AgB8/4 subunits in AgB oligomers of all samples analyzed. Quantitative and qualitative differences in the expression of AgB subunits were observed within and between samples. Using recombinant subunits as models, we showed that AgB subunits form distinct oligomeric states, with a rAgB8/3>rAgB8/2>rAgB8/1 maximum size relation. We also demonstrated by different experimental approaches that rAgB8/3 oligomers are more similar, both in size and morphology, to those observed for E. granulosus AgB. Overall, we provided experimental evidences that AgB is composed of different subunits within a single cyst, and that subunits have different abundances and oligomerization properties. These issues are important for the understanding of AgB expression and structure variations, and their impact for the host-parasite cross-talk. [ABSTRACT FROM AUTHOR]

Cowpea aphid-borne mosaic virus (CABMV) causes major diseases in cowpea and passion flower plants in Brazil and also in other countries. CABMV has also been isolated from leguminous species including, Cassia hoffmannseggii, Canavalia rosea, Crotalaria juncea and Arachis hypogaea in Brazil. The virus seems to be adapted to two distinct families, the Passifloraceae and Fabaceae. Aiming to identify CABMV and elucidate a possible host adaptation of this virus species, isolates from cowpea, passion flower and C. hoffmannseggii collected in the states of Pernambuco and Rio Grande do Norte were analysed by sequencing the complete coat protein genes. A phylogenetic tree was constructed based on the obtained sequences and those available in public databases. Major Brazilian isolates from passion flower, independently of the geographical distances among them, were grouped in three different clusters. The possible host adaptation was also observed in fabaceous-infecting CABMV Brazilian isolates. These host adaptations possibly occurred independently within Brazil, so all these clusters belong to a bigger Brazilian cluster. Nevertheless, African passion flower or cowpea-infecting isolates formed totally different clusters. These results showed that host adaptation could be one factor for CABMV evolution, although geographical isolation is a stronger factor. [ABSTRACT FROM AUTHOR]

Background: Citrus canker is a disease that has severe economic impact on the citrus industry worldwide. There are three types of canker, called A, B, and C. The three types have different phenotypes and affect different citrus species. The causative agent for type A is Xanthomonas citri subsp. citri, whose genome sequence was made available in 2002. Xanthomonas fuscans subsp. aurantifolii strain B causes canker B and Xanthomonas fuscans subsp. aurantifolii strain C causes canker C. Results: We have sequenced the genomes of strains B and C to draft status. We have compared their genomic content to X. citri subsp. citri and to other Xanthomonas genomes, with special emphasis on type III secreted effector repertoires. In addition to pthA, already known to be present in all three citrus canker strains, two additional effector genes, xopE3 and xopAI, are also present in all three strains and are both located on the same putative genomic island. These two effector genes, along with one other effector-like gene in the same region, are thus good candidates for being pathogenicity factors on citrus. Numerous gene content differences also exist between the three cankers strains, which can be correlated with their different virulence and host range. Particular attention was placed on the analysis of genes involved in biofilm formation and quorum sensing, type IV secretion, flagellum synthesis and motility, lipopolysacharide synthesis, and on the gene xacPNP, which codes for a natriuretic protein. Conclusion: We have uncovered numerous commonalities and differences in gene content between the genomes of the pathogenic agents causing citrus canker A, B, and C and other Xanthomonas genomes. Molecular genetics can now be employed to determine the role of these genes in plant-microbe interactions. The gained knowledge will be instrumental for improving citrus canker control. [ABSTRACT FROM AUTHOR]

The genera Daidalotarsonemus De Leon and Excelsotarsonemus Ochoa & Naskrecki are mainly characterized, in the females, by the presence of sculpturing on the dorsal shields and by highly modified dorsal setae, greatly enlarged, laminar or sail-shaped. Moreover, both genera are characterized by abundant cerotegument all over the body and on the modified setae (d , e , f) with the presence of fungi, lichens, and bacteria accumulating. The peculiar morphology of the dorsal setae in these two genera has suggested they might have other functions beside the sensory one. Ultrastructural observations using scanning and transmission electron microscopy techniques revealed that, albeit extravagantly modified, these dorsal setae should act as mechanoreceptors in agreement with most of the previous observations in mites. The morphological modifications of the setae d , e , and f (pronounced cup shape of setae e and enlarged shaft with concave longitudinal strips of setae d and f) suggest they play, in addition to the tactile function, a storage role and dispersive role for fungal spores collected by the mite while moving in the humid environment. Moreover, the modified setae d , e , and f inserted on elevated sockets are probably movable by the action of dorso-ventral muscles; thus, mites might use their sail-shape to become airborne. In addition, the body dorso-ventral muscles observed inserting close to the elevated seta e sockets suggest the mite might also lift these cup-like setae to spread the fungal particles on the body or over adjacent vegetation as well. Biological and feeding studies are necessary to better understand the role such fungi might play in the mite life cycle. • Posterior dorsal setae are highly modified in Daidalotarsonemus and Excelsotarsonemus females. • These setae don't have a hair shaft, are greatly enlarged or laminar. • According to their ultrastructure they are typical mechanoreceptive sensilla. • Their modified shaft seems to serve to store and carry fungal spores. • Mites seem able to rise the setae thanks to the contraction of dorso-ventral muscles attaching close to the seta sockets. [ABSTRACT FROM AUTHOR]

The knowledge of genomic data of new plant viruses is increasing exponentially; however, some aspects of their biology, such as vectors and host range, remain mostly unknown. This information is crucial for the understanding of virus–plant interactions, control strategies, and mechanisms to prevent outbreaks. Typically, rhabdoviruses infect monocot and dicot plants and are vectored in nature by hemipteran sap-sucking insects, including aphids, leafhoppers, and planthoppers. However, several strains of a potentially whitefly-transmitted virus, papaya cytorhabdovirus, were recently described: (i) bean-associated cytorhabdovirus (BaCV) in Brazil, (ii) papaya virus E (PpVE) in Ecuador, and (iii) citrus-associated rhabdovirus (CiaRV) in China. Here, we examine the potential of the Bemisia tabaci Middle East-Asia Minor 1 (MEAM1) to transmit BaCV, its morphological and cytopathological characteristics, and assess the incidence of BaCV across bean producing areas in Brazil. Our results show that BaCV is efficiently transmitted, in experimental conditions, by B. tabaci MEAM1 to bean cultivars, and with lower efficiency to cowpea and soybean. Moreover, we detected BaCV RNA in viruliferous whiteflies but we were unable to visualize viral particles or viroplasm in the whitefly tissues. BaCV could not be singly isolated for pathogenicity tests, identification of the induced symptoms, and the transmission assay. BaCV was detected in five out of the seven states in Brazil included in our study, suggesting that it is widely distributed throughout bean producing areas in the country. This is the first report of a whitefly-transmitted rhabdovirus. [ABSTRACT FROM AUTHOR]

Xantosoma riedelianum, also called "mangarito" in Brazil, is an unconventional food plant (UFP) of the Araceae family native to tropical America. Foliar samples of the X. riedelianum showing mosaic, mottle and vein clearing symptoms were collected in the municipality of Monte Alegre (São Paulo State). Transmission electron microscope observations, mechanical transmission to experimental plants, serological (DAS-ELISA) and RT-PCR analyzes indicated that the symptoms could be associated with the presence of dasheen mosaic virus (DsMV, Potyvirus). This is the first report of DsMV in X. riedelianum in Brazil. [ABSTRACT FROM AUTHOR]

The article presents a review of the reports made on Citrus leprosis, one of the most important diseases of the citrus industry in Brazil. It provides historical details and geographic distribution of citrus liprosis. It mentions that the first reported occurrence of Citrus leprosis started in Florida during the 20th century, and was reported in Brazil in the 1930s which was originally discovered in Navel sweet orange in Sorocaba, São Paulo in 1931.

Soybean stem necrosis is caused by Cowpea mild mottle virus (CPMMV) and it has been recognized as an emerging and economically important disease in Brazil. No resistant, but only tolerant cultivars have been identified so far, and their genetic control is still unknown. To investigate the inheritance of soybean tolerance to CPMMV, two crosses between tolerant cultivars (BRS 133 x BRSMT Pintado), and between a susceptible (CD 206) and a tolerant cultivar (BRSMT Pintado) were carried out to obtain F2 and F2:3 generations. Quantitative and qualitative analyses applied to the data from greenhouse evaluations showed that there are at least two distinct major genes determining tolerance to CPMMV, one in the soybean cultivar BRS 133 and another in the cultivar BRSMT Pintado, with predominance of additive genetic effects and heritability levels that allow for efficient selection based on early generation means. [ABSTRACT FROM AUTHOR]

A new symptomatology was observed in celery (Apium graveolens) in Villena, Spain in 2008. Symptomatology included an abnormal amount of shoots per plant and curled stems. These vegetative disorders were associated with 'Candidatus Liberibacter solanacearum' and not with phytoplasmas. Samples from plant sap were immobilized on membranes based on the spot procedure and tested using a newly developed real-time polymerase chain reaction assay to detect 'Ca. L. solanacearum'. Then, a test kit was developed and validated by intralaboratory assays with an accuracy of 100%. Bacterial-like cells with typical morphology of 'Ca. Liberibacter' were observed using electron microscopy in celery plant tissues. A fifth haplotype of 'Ca. L. solanacearum', named E, was identified in celery and in carrot after analyzing partial sequences of 16S and 50S ribosomal RNA genes. From our results, celery (family Apiaceae) can be listed as a new natural host of this emerging bacterium. [ABSTRACT FROM AUTHOR]

Abstract: A decade ago, a new mite-transmitted disease was described on wheat (Triticum aesativum) and maize (Zea mays) that due to its geographical location was referred to as High Plains Disease (HPD). To determine the etiology, we established colonies of HPD pathogen-transmitting eriophyid wheat curl mites (Aceria tosichella) on wheat plants for maintenance of a continuous source of infected material. Analyses of nucleic acid obtained from infected plants showed the presence of HPD-specific RNAs ranging from 1.5 to 8 kilobases, but comparisons between the sequence of cDNAs and the databases did not reveal any clear identity with known viruses. We demonstrate that a diagnostic HPD-specific 32-kDa protein that accumulates in plants is encoded by a small RNA species (RNA-s). Upon infestation of upper wheat parts with viruliferous mites, the RNA-s encoded protein becomes detectable within a few days in the roots, indicative of an effective virus-like mode of transport. Membranous particles, resembling those observed in thin sections of infected plants, were isolated and shown to envelope a thread-like ribonucleoprotein complex containing the RNA-s encoded 32-kDa protein. This complex was associated with single-stranded (−)-sense RNAs, whereas free (+)-sense RNA was only detected in total RNA of infected plants. Based on the collective properties, we conclude that HPD is caused by a newly emerged mite-borne virus, for which we propose the name Maize red stripe virus (MRStV). [Copyright &y& Elsevier]

Citrus sudden death (CSD) is a new disease that has killed approximately 1 million orange trees in Brazil. Here we report the identification of a new virus associated with the disease. RNAs isolated from CSD-affected and nonaffected trees were used to construct cDNA libraries. A set of viral sequences present exclusively in libraries of CSD-affected trees was used to obtain the complete genome sequence of the new virus. Phylogenetic analysis revealed that this virus is a new member of the genus Marafivirus. Antibodies raised against the putative viral coat proteins allowed detection of viral antigens of expected sizes in affected plants. Electron microscopy of purified virus confirmed the presence of typical isometric Marafivirus particles. The screening of 773 affected and nonaffected citrus trees for the presence of the virus showed a 99.7% correlation between disease symptoms and the presence of the virus. We also detected the virus in aphids feeding on affected trees. These results suggest that this virus is likely to be the causative agent of CSD. The virus was named Citrus sudden death-associated virus. [ABSTRACT FROM AUTHOR]

Citrus leprosis virus (CiLV), a tentative member of the Rhabdoviridae family, affects citrus trees in Brazil, where it is transmitted by mites Brevipalpus spp. It also occurs in other South American countries and was recently identified in Central America. This northbound spread of CiLV is being considered a serious threat to the citrus industry of the United States. However, despite its importance, difficulties related to the biology of CiLV have hindered much of the progress regarding its accurate detection, leaving both the analyses of symptoms and electron microscopy as the only tools available. An attempt to overcome this problem was made by constructing a cDNA library from double-stranded RNA extracted from leprosis lesions of infected Citrus sinensis (sweet orange) leaves. After cloning and sequencing, specific primers were designed to amplify putative CiLV genome regions with similarity to genes encoding the movement protein and replicase of other plant viruses. RNA from infected citrus plants corresponding to different varieties and locations were amplified by reverse transcription polymerase chain reaction (RT-PCR) using the two pairs of primers. Amplified products were purified, cloned in pGEM-T, and sequenced. The sequences confirmed the genomic regions previously associated with CiLV. The results demonstrate that RT-PCR was specific, accurate, rapid, and reliable for the detection of CiLV. [ABSTRACT FROM AUTHOR]